What is it about?
As electron diffraction can be done on nanoscale particles, we tried whether we could determine the precise structure before and after charging by using the intensities in quantitative electron diffraction patterns to solve and refine those crystal structures. The in situ charging was done using a commercial holder. Our own background expertise was the use of the EDT (electron diffraction tomography) method on various materials for solving and refining their structures, but up to this paper only using ex situ data.
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Why is it important?
In situ experiments on lithium battery cathode materials are hindered by the small size of the particles and by secondary phases when using X-rays or neutrons. However, using electrons you can choose the nanosized particle to work on and ignore all the rest. Thus such experiments can in this case provide single crystal data where X-rays and neutrons can only provide multiphase powder diffraction data. We think that this method should allow in the future to obtain valuable data on the evolution of crystal structures during cycling.
Perspectives
When you compare it to TEM imaging techniques, EDT (and other 3D ED techniques, or other labels like Micro-ED) does not give information for separate specific atoms or colums, but it gives information on the average structure of the volume from which diffraction is taken. This is on the one hand more representative, on the other hand off course it does not give a direct visualization of local effects. It also does not need a high electron dose and is thus less likely to influence the results than imaging techniques. Especially for in situ experiments in liquid, such as for these electrochemistry reactions, imaging is limited as the resolution is worsened by the liquid, whereas for electron diffraction the liquid causes just an overall weakening of the intensities. Also diffraction has no problem with the on-growth of (probably) amorphous nanoparticles, which we dis see in direct space but gave us no trouble in reciprocal space. However, there are many challenges to making this a standard technique: so far the main challenge in our experiments (published and ongoing), is that the liquid is too thick to allow to acquire good ED patterns when the cell is completely filled. We are currently working on finding ways to solve this (anno 2020).
Prof. Dr. Joke Hadermann
Universiteit Antwerpen
Read the Original
This page is a summary of: In Situ Electron Diffraction Tomography Using a Liquid-Electrochemical Transmission Electron Microscopy Cell for Crystal Structure Determination of Cathode Materials for Li-Ion batteries, Nano Letters, September 2018, American Chemical Society (ACS),
DOI: 10.1021/acs.nanolett.8b02436.
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